[GlobalsModRef][FIX] Ensure we honor synchronizing effects of intrinsics

This is a long standing problem that resurfaces once in a while [0].
There might actually be two problems because I'm not 100% sure if the
issue underlying https://reviews.llvm.org/D115302 would be solved by
this or not. Anyway.

In 2008 we thought intrinsics do not read/write globals passed to them:
https://github.com/llvm/llvm-project/commit/d4133ac31535ce5176f97e9fc81825af8a808760
This is not correct given that intrinsics can synchronize threads and
cause effects to effectively become visible.

NOTE: I did not yet modify any tests but only tried out the reproducer
      of https://github.com/llvm/llvm-project/issues/54851.

Fixes: https://github.com/llvm/llvm-project/issues/54851

[0] https://discourse.llvm.org/t/bug-gvn-memdep-bug-in-the-presence-of-intrinsics/59402

Differential Revision: https://reviews.llvm.org/D123531